That's a neat idea. Yes, slipping the stitch at the markers will help it fold and when it's all knit you close off the ends. I think I'll start tossing odds and ends of yarn in a big garbage bag. At least that way I'll think I'm going to do something with them as they are and quit trying to figure out what to do with them.
I've seen suggestions that you can work a few rows flat and then join to avoid the mobius effect. With that many stitches, I think I would.
I should never overestimate my basic arithmetic skills.